Vacationing in France, disenchanted British teacher John Barrett (Alec Guinness) meets nobleman Jacques De Gué (Guinness), who could be his twin. Fascinated, John accompanies Jacques to his hotel for drinks and passes out. The next morning, Jacques has vanished. His chauffeur mistakes John for him and takes him to the De Gué chateau. There, John is drawn into the lives of Jacques' bedridden mother, unbalanced wife and lovely mistress, unaware of the nobleman's nefarious plans for his double.